Insulating material



UNITED STATES PATENT orrlcs.

LEON MOCULLOCH, OF WILKINSBURG, PENNSYLVANIA, ASSIGNOR TO WESTING- HOUSE ELECTRIC AND MANUFACTURING COMPANY, A CORPORATION OF Patented Aug. 2, 1921.

PENNSYLVANIA I INSULATING MATERIAL.

1,386,008. Specification of Letters Patent.

No Drawing.

To all whom it may concern:

Be it known that I, LEON MoCULLooH, a citizen of the UnitedStates, and a resident of Wilkinsbur in the county of Allegheny and State of ennsylvania, have invented a new and useful Improvement in Insulating Material, of which the following is a specification.

My invention relates to composite electrical insulating material consisting of a binder and flake material such as mica, and it has for its object to provide a composite material comprising a bond of a permanent nature, which shall be unaflected by heat Within normal operating ranges and shall have no tendency to soften or shrink at such operating temperatures.

The bond which I prefer to employ for the urpose indicated consists of boron trioxid or some other oxygen compound of boron, with or without the addition of fillers or other ingredients. According to one meth- 0d of applying my invention, mica flakes or mica spllttings are built up into a plate of the required thickness, dry powdered boric acid or a boric acid compound, such as ammonium borate, being sprinkled between the successive layers of mica. The built-up plate is then baked under pressure at a temperature of 500 C. or less, thereby fusing and substantially dehydrating the-boric acid and decomposing the ammonium borate, if the latter compound is employed, leaving fused boric oxid containing only small amounts of water and gases.

The foregoing process may be varied by applying boric acid or a boric acid compound, such as ammonium borate, in admixture with a liquid such as benzin or very thin varnish which does not dissolve the boric material, but only serves as a vehicle for spreading the boric material between the mica flakes; or the boric acid, ammonium borate or other boric acid compound may be applied in solution in water, alcohol or other solvent. The vehicle or the solvent will be driven off, either wholly or in part, by the subsequent heat treatment. Other ingredients may be added to the bonding material for increasing its adhesiveness or bulk, suitable materials for this purpose being shellac or other varnish gums and finely divided inorganic materials such as clays of the bentonite type, kaolin, metallic oxids' and the like.

Application filed January 5, 1917. Serial No. 140,822.

One bonding mixture which I have eniployed with good results is prepared by mixing dry boric acid or ammonium borate with a small amount of bentonite filler and workmg to a thin paste with a water solution of glycerin. The glycerin reacts with the boric acid present to form a sticky glyceryl borate 'whlch renders the entire mixture adhesive and effectually holds the mica flakes together during the building-up process. When heat is applied to the composite material, the glycerin is driven off, and the boric oxid which remains behind acts as the final bond. Boric oxid imparts to composite materials containing it the property of softening at moderately elevated temperatures of the order of 500 (3., but since the boric oxid does not become completely fluid except at temperatures several hundred degrees above this point, the composite material is entirely coherent at all temperatures ordinarily encountered in the o eration of electrical apparatus. Boric oxid binders have the further advantage that they do not exert a de structive fluxing action upon mica, as do many of the binding materials which have heretofore been employed for the purpose of making composite insulating materials.

It is to be understood that my invention '1. A composite material comprising flake material and a lead free binder containing an ox gen compound of boron.

2. composite material comprising flake material and a lead free binder containing boron trioxid.

3. A composite material comprising flake" material and a lead .free binder containing an ox gen compound.- of boron and a filler.

4. composite material comprising flake material and a lead free binder comprising boron trioxid and a pulverulent filler.

5. A com osite material comprising mica flakes or splittings held together by means of a lead free binder containing an oxygen compound of boron and a filler.

6. A com osite material comprising mica flakes or, sp ittings held together by means of a lead free binder containing boron trioxid.

7. A composite material comprising mica flakes or s littings held together by means of a lead res binder containing boron trioxid and a pulverulent filler.

8. A process of making composite material that comprises associating flake material with an adhesive lead free binder containing an oxygen compound of boron, and applying heat and pressure to the said materia 9. A process of making composite material that comprises associating flake material with a binder formed b mixing boric acid water and g1 cerin, an applying heat and pressure to tlie said material.

10. A process of making composite material that comprises superposin mica flakes or splittings coated with a bin er formed by mixlng boric acid, water and glycerin, and heating the superposed flakes or splittin to a temperature not exceeding 500 C.

11. A process of making composite material that comprises superposin mica flakes or splittings coated with a bin er formed by mixing boric acid, water, lycerin and a pulverulent filler, and heating the superposed flakes or splittings to not exceedin 500 C.

12. A bin or for use in composite materials comfrising an oxygen compound of bloron an a small amount of a pulverulent c ay. v

13. A binder for use in composite materials comprising 'a com ound of boron, a pulverulent clay filler an d glycerin.

14. A'binder 'for use in composite materials comprising an oxygen compound of boron, a bentonite clay as a filler and glycarm.

15. The composite material resulting from subjecting to heat and pressure mica flakes or splits associated with a binder comlprising an oxy en compound of boron and g ycerin.

16. he composite material resulting from subjecting to heat and pressure mica flakes or splits associated with a binder comprisin an oxygen com ound of boron and a sma 1 amount of a pu verulent clsiy as a filler.

In testimony whereof, have hereunto subscribed my name this 27th day of Dec, 1916.

a temperature LEON MOOULLOOH. 

